1. Field of the Invention
The present invention relates to an optical element positioning device for positioning optical elements such as an objective lens, a prism, and an optical filter.
2. Description of the Related Art
Generally, an optical path switching device for an optical microscope is known as an optical element positioning device used in an optical microscope. In this optical path switching device, a revolver which includes various detachable objective lenses different in magnification is rotated to interchange the objective lenses with respect to the optical axis, thereby switching the magnifications. Also, a turret condenser in which a plurality of ring stops or iris stops for a bright field are concentrically arranged is incorporated into the microscope main body so as to be freely inserted and removed. The combination of these mechanisms makes it possible to handle a broad range of objective lenses.
Jpn. UM. Appln. KOKAI Publication No. 51-70545 describes an optical element interchanging device of an optical microscope, in which a revolver includes a locking mechanism for positioning an objective lens on the optical axis. FIG. 9 shows this locking mechanism of the revolver.
A rotating ring 2 is rotatably attached to a revolver main body 1 of an optical microscope. Between the outer circumferential portion of the revolver main body 1 and the inner circumferential portion of the rotating ring 2, a press ring 3 fixed to the rotating ring 2 is provided. A large number of balls 4 are placed between the lower surface of the press ring 3 and the upper surface of the outer circumferential portion of the revolver main body 1, constituting a ball bearing.
A ball 5 is held in a recess formed in the rotation center of the rotating ring 2. This ball 5 is pressed with a predetermined force by a press screw 6 which is threadably engaged to extend through the revolver main body 1 from its upper surface. Thus the ball 5 is clamped between the press screw 6 in the revolver main body 1 and the recess of the rotating ring 2.
With the above structure, the rotating ring 2 is held by the revolver main body 1 so as to be rotatable around the ball 5.
A locking mechanism for positioning the rotating ring 2 at a predetermined angular position has a leaf spring 8. A steel ball 7 is supported at the distal end portion of the leaf spring 8, and a proximal end portion 9 of the leaf spring 8 is fixed on the upper surface of the revolver main body 1. Annular guide portion 10 integrally projects from the upper surface near the outer circumference of the rotating ring 2. V-grooves 10a are formed at positions on the upper surface of the guide portion 10 which correspond to the stop positions of individual objective lenses 16 different in magnification. The steel ball 7 is pressed against the upper surface of the guide portion 10 by the leaf spring 8.
In the above locking mechanism, when the selected one of the objective lenses 16 comes close to the optical axis upon rotation of the rotating ring 2, the steel ball 7 is drawn to the selected V-groove 10a and dropped into it by the biasing force of the leaf spring 8. As a result, the rotating ring 2 is stopped with no rocking motion by the biasing force of the leaf spring 8, and the desired objective lens 16 is positioned on the optical axis accordingly.
In the locking mechanism described above, there is a variation in the biasing force of the leaf spring 8 before and after the steel ball 7 is dropped into the V-groove 10a. Consequently, an impact force is produced when the steel ball 7 is quickly pushed into the V-groove 10a. This impact force is felt by an observer when he or she switches the objective lenses 16 by rotating the rotating ring 2. The observer, therefore, can confirm that the desired objective lens 16 is positioned on the optical axis.
Jap. Pat. Appln. KOKAI Publication No. 55-159214 describes an optical element interchanging device of an optical microscope, which includes a click stop mechanism which moves and stops, at equal pitches, a movable member using a magnetic attracting element. FIG. 10 illustrates this click stop mechanism.
On the upper surface of a fixed plate 11 of a stationary member of this mechanism, a plurality of permanent magnets 12 are arranged at equal pitches so that the magnetic poles on the upper surfaces of the neighboring magnets are opposite to each other. A pair of parallel guides 13 are disposed parallel to the upper surface of the fixed plate 11, i.e., the upper surfaces of the permanent magnets 12 with a predetermined distance between them, extending in the direction of arrangement of these permanent magnets. A movable plate 14 is slidably mounted on these guides 13. This movable plate 14 includes a pair of permanent magnets 15 on the surface opposing the permanent magnets 12 of the fixed plate 11. These permanent magnets 15 have opposite magnetic poles on their lower surfaces. The movable plate 14 is slid along the guides 13 either manually or automatically.
In the above structure, while the movable plate 14 is sliding if the magnetic pole of the permanent magnet 12 of the fixed plate 11 and the magnetic pole of the permanent magnet 15 of the movable plate 14 sliding along the guides 13 become opposite to each other between the opposing surfaces, it is possible to stop the movable plate 14 sliding along the guides 13 by the action of the magnetic attracting force produced between the opposite magnetic poles. On the other hand, if the magnetic pole of the permanent magnet 12 of the fixed plate 11 and the magnetic pole of the permanent magnet 15 of the movable plate 14 agree with each other between the opposing surfaces, it is possible to rapidly slide the movable member 14 by the action of the magnetic repulsing force produced between the two magnetic poles.
One recently known device uses an inverted optical microscope including a revolves positioned under a stage having the locking mechanism in combination with a micromanipulator to perform various micromanipulations for cells (e.g., gripping, piercing, injection, and cut) in addition to observation of cells.
Unfortunately, in performing manipulations by using the combination of the optical microscope and the micromanipulator, a manipulator needle which is already positioned for micromanipulations is moved by the impact force produced when the objective lens is positioned.
Additionally, if the steel ball 7 is constantly urged against the upper surface of the annular guide portion 10 by the biasing force of the leaf spring 8, the V-groove 10a is gradually abraded. This weakens the touch when the objective lens 16 is positioned or decreases the positioning accuracy.
Also, in the click stop mechanism shown in FIG. 10, in performing multi-pole magnetization for the permanent magnets 12 provided on the fixed plate 11 there is produced a partial difference in the strength between the magnetic forces or a slight difference in the boundary position between the N and S poles. The result is a difference in the magnetic attracting force between the permanent magnets 12 of the fixed plate 11 and the permanent magnets 15 of the movable plate 14. This makes accurate positioning impossible.